This invention relates to methods of leaching metals from metal-containing particles, such as spent hydroprocessing catalysts.
One modern development in crude oil processing is the upgrading of metal- and sulfur-containing feedstocks (e.g., crude oils and residua) by hydroprocessing methods. Such upgrading is necessary to convert the heavy feedstock into more valuable, lower boiling fractions and to remove metals and sulfur contaminants that can pollute the atmosphere upon combustion.
Crude oils contain various dissolved contaminants, including nickel, vanadium, iron, and sulfur. The lighter fractions are frequently distilled off under either atmospheric pressure or a partial vacuum, leaving the metals in a high boiling fraction called the "residua." Residua will generally contain at least 35 ppm metal contaminants, frequently as high as 100 ppm, and in extreme cases, higher than 1000 ppm.
These metals, and any sulfur present, are removed by processing the feedstock with a catalyst in the presence of hydrogen. Such catalysts are generally a solid support that contains catalytic metals, generally a Group VIII metal alone or in conjunction with a Group VI metal. The Group VI metal is typically tungsten or molybdenum and the Group VIII metal is typically nickel or cobalt. As the catalyst is used, metals from the feedstock deposit on its exterior surface and the interior surface of its pores, eventually plugging the pores and reducing the activity of the catalyst to such an extent it does not give the desired product quality. Such catalysts are herein defined as "spent catalysts," and contain catalytic metals, an inorganic support matrix, metals removed from the feedstock, sulfur compounds, and a hydrocarbonaceous residuum.
Recently, the obtainable crude oil is tending to be heavier, forcing refiners to use more hydroprocessing catalysts than heretofore necessary to remove metals and sulfur from the feedstock. It is therefore possible that a shortage will develop of the valuable catalytic metals, particularly cobalt. Efforts have been made to extract metals from hydroprocessing catalysts so that the catalytic metals, the deposited metals, and the catalyst supports can be reused.
One process of leaching hydroprocessing catalysts is disclosed in U.S. Pat. No. 3,567,433. An aqueous ammonia and ammonium salt leach solution is contacted with spent catalyst particles.
Another leaching process is disclosed in Chemical Abstracts, 94: 178649x. A spent catalyst, containing aluminum, vanadium, nickel, cobalt, and molybdenum, was leached with ammonia and ammonium salts, at a temperature greater than 110.degree. C. and an oxygen partial pressure of greater than 1 kg/cm.sup.2, for more than 1/2 hour. Such conditions require autoclave reactors.
U.S. Pat. No. 4,216,118 discloses chlorinating spent catalysts to convert vanadium values to vanadium tetrachloride and nickel values to nickel chloride for recovery by solvent extraction.
U.S. Pat. No. 4,145,397 discloses recovery of metals from spent catalysts by roasting at high temperatures and leaching with caustic alkali.
U.S. Pat. No. 4,432,949 discloses separating metal values from an aqueous stream containing vanadium, molybdenum, nickel, and cobalt. Vanadium is first precipitated, and then nickel, cobalt, and molybdenum are removed by serial ion exchange.
U.S. Pat. No. 4,434,141 discloses recovering metal values from an aqueous stream. The metal values are preferably obtained from leaching spent hydroprocessing catalysts, and include nickel, cobalt, vanadium, and molybdenum. The metal values are extracted, isolated, and purified by liquid, liquid extraction techniques.
An article in Engineering and Mining Journal, May 1978, page 105, describes a plant to process spent catalysts containing no cobalt by first leaching with sodium hydroxide and then with ammonium carbonate.
It would be advantageous if a method were found for leaching, simultaneously, cobalt and molybdenum, nickel, and vanadium from hydroprocessing catalysts with high yields of each metal value.